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71.
Anurag Gupta Somnath Chattopadhyaya Sergej Hloch 《Rock Mechanics and Rock Engineering》2013,46(1):169-177
Mining and petroleum drill bits are subjected to highly abrasive rock and high-velocity fluids that cause severe wear and erosion in service. To augment the rate of penetration and minimize the cost per foot, such drill bits are subjected to increasing rotary speeds and weight. A rotary/percussive drill typically hits the rock 50 times per second with hydraulic impact pressure of about 170–200 bar and feed pressure of about 90–100 bar, while rotating at 75–200 rpm. The drill rig delivers a high-velocity flow of drilling fluid onto the rock surface to dislodge cuttings and cool the bit. The impingement of high-velocity drilling fluid with entrained cuttings accelerates the erosion rate of the bit. Also, high service temperature contributes to softening of the rock for increased penetration. Hence, there is a need to optimize the drilling process and balance the wear rate and penetration rate simultaneously. This paper presents an experimental scanning electron microscopy (SEM) study of electroplated (nickel-bonded) diamond drills for different wear modes. 相似文献
72.
Biswajit Pandey Somnath Bharadwaj 《Monthly notices of the Royal Astronomical Society》2008,387(2):767-771
We have quantified the average filamentarity of the galaxy distribution in seven nearly two-dimensional strips from the Sloan Digital Sky Survey Data Release Five (SDSS DR5) using a volume-limited sample in the absolute magnitude range −21 ≤ M r ≤−20 . The average filamentarity of star-forming (SF) galaxies, which are predominantly blue, is found to be more than that of other galaxies which are predominantly red. This difference is possibly an outcome of the fact that blue galaxies have a more filamentary distribution. Comparing the SF galaxies with only the other blue galaxies, we find that the two show nearly equal filamentarity. Separately analyzing the galaxies with high star formation rates (SFR) and low SFR, we find that the latter has a more filamentary distribution. We interpret this in terms of two effects. (i) A correlation between the SFR and individual galaxy properties like luminosity with the high-SFR galaxies being more luminous. (ii) A relation between the SFR and environmental effects like the density with the high-SFR galaxies preferentially occurring in high-density regions. These two effects are possibly not independent and are operating simultaneously. We do not find any difference in the filamentarity of SF galaxies and active galactic nuclei. 相似文献
73.
We develop an approach to deriving the three-dimensional non-force-free coronal magnetic field from vector magnetograms. Based
on the principle of minimum dissipation rate, a general non-force-free magnetic field is expressed as the superposition of
one potential field and two constant-α (linear) force-free fields. Each is extrapolated from its bottom boundary data, providing the normal component only. The
constant-α parameters are distinct and determined by minimizing the deviations between the numerically computed and measured transverse
magnetic field at the bottom boundary. The boundary conditions required are at least two layers of vector magnetograms, one
at the photospheric level and the other at the chromospheric level, presumably. We apply our approach to a few analytic test
cases, especially to two nonlinear force-free cases examined by Schrijver et al. (Solar Phys.
235, 161, 2006). We find that for one case with small α parameters, the quantitative measures of the quality of our result are better than the median values of those from a set
of nonlinear force-free methods. The reconstructed magnetic-field configuration is valid up to a vertical height of the transverse
scale. For the other cases, the results remain valid to a lower vertical height owing to the limitations of the linear force-free-field
solver. Because our method is based on the fast-Fourier-transform algorithm, it is much faster and easy to implement. We discuss
the potential usefulness of our method and its limitations. 相似文献
74.
James?EguchiEmail author Rajdeep?Dasgupta 《Contributions to Mineralogy and Petrology》2017,172(2-3):12
We have performed experiments to determine the effects of pressure, temperature and oxygen fugacity on the CO2 contents in nominally anhydrous andesitic melts at graphite saturation. The andesite composition was specifically chosen to match a low-degree partial melt composition that is generated from MORB-like eclogite in the convective, oceanic upper mantle. Experiments were performed at 1–3 GPa, 1375–1550?°C, and fO2 of FMQ ?3.2 to FMQ ?2.3 and the resulting experimental glasses were analyzed for CO2 and H2O contents using FTIR and SIMS. Experimental results were used to develop a thermodynamic model to predict CO2 content of nominally anhydrous andesitic melts at graphite saturation. Fitting of experimental data returned thermodynamic parameters for dissolution of CO2 as molecular CO2: ln(K 0) = ?21.79?±?0.04, ΔV 0?=?32.91?±?0.65 cm3mol?1, ΔH 0?=?107?±?21 kJ mol?1, and dissolution of CO2 as CO3 2?: ln(K 0 ) = ?21.38?±?0.08, ΔV 0?=?30.66?±?1.33 cm3 mol?1, ΔH 0?=?42?±?37 kJ mol?1, where K 0 is the equilibrium constant at some reference pressure and temperature, ΔV 0 is the volume change of reaction, and ΔH 0 is the enthalpy change of reaction. The thermodynamic model was used along with trace element partition coefficients to calculate the CO2 contents and CO2/Nb ratios resulting from the mixing of a depleted MORB and the partial melt of a graphite-saturated eclogite. Comparison with natural MORB and OIB data suggests that the CO2 contents and CO2/Nb ratios of CO2-enriched oceanic basalts cannot be produced by mixing with partial melts of graphite-saturated eclogite. Instead, they must be produced by melting of a source containing carbonate. This result places a lower bound on the oxygen fugacity for the source region of these CO2-enriched basalts, and suggests that fO2 measurements made on cratonic xenoliths may not be applicable to the convecting upper mantle. CO2-depleted basalts, on the other hand, are consistent with mixing between depleted MORB and partial melts of a graphite-saturated eclogite. Furthermore, calculations suggest that eclogite can remain saturated in graphite in the convecting upper mantle, acting as a reservoir for C. 相似文献
75.
The finite element method was used to solve the problem of flow to a partially penetrating strainer well in a leaky confined aquifer under steady and unsteady conditions. Predictions of the model were compared with reported pumping test data. A good agreement was obtained between them. The effects of penetration and screen position on discharge through imperfect well were studied. Results were compared with analytical solutions and presented graphically. 相似文献
76.
77.
Summary A reconnaissance paleomagnetic study of Hispaniola shows that three igneous units in the Dominican Republic possess meaningful directions of magnetism. A Late Cretaceous tonalite, an Eocene pyroxene diorite and a Miocene andesite porphyry have been investigated. The rock material studied is fresh, and has not been affected by secondary oxidation except in the case of the andesite which is occasionally weathered and reveals some hydrothermal alteration. Alternating field and thermal demagnetization result in removal of viscous remanence in some samples, while others reveal a good stability of NRM and little change in direction. The results disclose directions of magnetization substantially different from that of the present earth's field in Hispaniola and from those obtained from contemporaneous rocks of North America. They yield paleomagnetic poles at 23.1° N, 144.9° W for the Cretaceous tonalite and at 17.4° N, 138.0° W for the Eocene diorite, the positions of which are not significantly different from each other, suggesting no change of geomagnetic field direction during the two epochs. These poles have generally similar positions to those obtained from Late Cretaceous rocks on Jamaica and Puerto Rico. The Miocene data fall into two groups, one having a direction corresponding to a pole closely coinciding with the Miocene North American pole and the other giving a paleomagnetic pole at 68.3° N, 151.9° W coinciding with the Miocene pole for Jamaica. Paleotectonic interpretation of the results suggests that like other Greater Antilles, Hispaniola has been subject to large anticlockwise rotation since Late Cretaceous. 相似文献
78.
H.C Dasgupta 《Lithos》1978,11(2):121-131
R-mode factor analysis of modal and chemical data clarifies the trends of mineralogical evolution and associated chemical variations in amphibolites from the Northwest Adirondack Mountains, New York and the Willyama Complex, Broken Hill District. In both areas the principal mineralogical reaction attending metamorphism, as described by the first factor, appears to have been Hornblende + Quartz → Calcic pyroxene + Orthopyroxene + Plagioclase. For the Adirondack amphibolites, the derived reaction coefficients viewed against the modal contents of the pyroxenes suggest another hornblende breakdown reaction producing calcic pyroxene, which is corroborated by the first appearance of the phase a little NE of Emeryville. The other factors extracted reveal the underlying parameters responsible for the development of biotite, sphene, opaques and quartz in the Adirondack metabasites and albite, anorthite, ilmenite and quartz in the Willyama Complex amphibolites.The analysis also demonstrates that the principal mineralogical reactions in both the areas have been combinations of thermal and ionic types and further that to decipher the net mineralogical changes in high grade metamorphic basic and pelitic rocks it is necessary to extend the integration of the ‘part reactions’ occurring in different domains to the level of a hand specimen. 相似文献
79.
Chemical composition of the phases occurring as corona structures in the Thessaloniki gabbros are subjected to algebraic method of treatment following Korzhinskii [1]. The analysis reveals that the mineralogical reactions responsible for the growth of the corona structures were possibly allochemical in nature in regard to the non-volatile components. The chemical similarity of the pyroxenes occurring within and beyond the corona structures in the gabbros appears compatible with such a model. 相似文献
80.
Stability of manganocordierite and related phase equilibria in part of the system MnO-Al2O3-SiO2-H2O
The pressure temperature stability of the phase Mn-cordierite hitherto not recorded as a mineral has been determined at temperatures ranging from 400° C up to the melting mainly using standard hydrothermal techniques at the oxygen fugacities provided by the buffering power of the bomb walls. Manganocordierite is a pronounced low-pressure phase with a maximum pressure stability of about 1 kb near 400° C and decreasing pressure limits at higher temperatures. Throughout the temperature range investigated the stable high-pressure breakdown assemblage of Mn-cordierite is spessartine, an Al-silicate, and a SiO2-polymorph. Due to the variable water contents of Mn-cordierite and spessartine there is a pronounced curvature in the negative dP/dT-slope of the requisite upper pressure breakdown curve of Mn-cordierite. Only theoretical deductions were possible concerning the stable hydrous low-temperature breakdown assemblage of Mn-cordierite below about 400° C.The manganocordierites synthesized are orthorhombic low-cordierites with distortion indices increasing with temperature, water pressure, and duration of heating. Their mean refractive indices increase with rising contents of absorbed water in the structural channels. Based on experiments with natural material the upper temperature stability limit of the mineral carpholite must lie at temperatures below about 400° C for water pressures up to 2.5 kb.The absence of Mn-cordierite from natural rocks studied thus far cannot be explained on chemical grounds, but must be due to its narrow pressure temperature stability range. The phase may yet be discovered as a mineral in manganiferous metasediments formed by lowpressure contact metamorphism. 相似文献